Field of the Invention
This invention relates generally to imaging devices, and more particularly to an avalanche photodiode-based imaging device capable of imaging in at least two distinct wavebands.
Description of the Related Art
Imaging in two distinct wavebands (e.g., midwave-longwave or visible-midwave) typically requires multiple focal plane arrays. The most advanced focal plane arrays can image two wavebands separately, but typically can only measure one waveband at a time and must dither between the two wavebands to produce a two color image.
In other instances, simultaneous two color imaging is possible. However, this requires complex fabrication techniques as well as the need for pixels sensitive to different colors to have their own separate electrical connections to the readout integrated circuit (ROIC). This is illustrated in FIG. 1. Two p-n junction devices 10 and 12 are designed to image two different wavebands. For example, device 10 may be arranged to image incoming light with wavelengths 14 in the blue or UV portions of the spectrum, and device 12 may be arranged to image incoming light with wavelengths 16 in the red or IR portions of the spectrum. Each device would typically require an indium bump 18, 20 to facilitate connection to an ROIC. This requirement for a separate electrical connection to the ROIC for different colors comes at the expense of decreased focal plane array format size or an increase in system size, weight and power (SWaP). In addition, to be sensitive to different wavelengths, each photodiode may need to be based on different materials and require different fabrication steps.